Stegosaurs back plates ‘reveal sex’

Male and female Stegosaurs may have had different-shaped back plates, the distinctive feature that makes the famous dinosaur so recognisable, scientists believe.

Evidence suggests females had tall, pointy plates while males had wider curved plates that were up to 45% larger.

The research, published in the online journal Public Library of Science ONE, may shed light on the sex of the Natural History Museum’s Stegosaurus known as Sophie.

The dinosaur’s almost-complete skeleton recently took pride of place inside the London museum’s Exhibition Road entrance.

But despite the Sophie nickname, after the daughter of the donor who made the acquisition possible, the 150 million-year-old creature’s gender remains a mystery.

The new research is based on findings from a Stegosaurus “graveyard” in central Montana, US, which yielded specimens with the two different kinds of bony back plates.

British dinosaur scientist Evan Saitta, from the University of Bristol, carried out a CT scan and microscope analysis which showed that the differences were not due to growth or to specimens belonging to different species.

He believes the larger plates can be compared with the manes of male lions.

Mr Saitta said: “As males typically invest more in their ornamentation, the larger, wide plates likely came from males. These broad plates would have provided a great display surface to attract mates.

“The tall plates might have functioned as prickly predator deterrents in females. These Stegosaurs seem to provide the first really convincing evidence for sexual dimorphism in a dinosaur species (excluding birds, which are technically dinosaurs themselves).”

The Natural History Museum’s chief dinosaur expert Paul Barrett is not entirely convinced.

He said: “I’d like to see a lot more information on the graveyard site itself, the different sizes of the specimens, how they were arranged in the ground, more detail on the geology, and on the analyses that were done.

“But it is interesting because it would add to the debate on what the plates were for. Sexual dimorphism is something we see a lot in modern animals, although it’s not particularly prevalent in living reptiles or in living birds.”